It is becoming increasingly attractive to use nodes in a wireless network as relaying points to extend range and/or increase power efficiency of wireless transmissions. For example, in a wireless local area network (WLAN), network devices may be configured to receive and forward communications which are ultimately destined for a different device. These types of networks are generically referred to as “mesh” networks, where network nodes may form a “mesh” of paths for which communications may travel to reach their destination.
Wireless networks may use beacon transmissions to advertise the network's existence, as well as provide information about the network and capabilities associated with the network.
Various beaconing techniques have previously been used in wireless networks. For example, the Institute of Electrical and Electronics Engineers (IEEE) IEEE Std. 802.11-1997 specifies the use of two different kinds of beaconing mechanisms; one for infrastructure mode networks (also called basic service set (BSS) networks) and one for ad-hoc mode networks (also called independent basic service set (IBSS) networks)
In infrastructure networks, access points (APs) are the entities responsible for generating beacons whereas in ad hoc networks all network nodes (including user stations) participate in the generation of beacons. The ad hoc network beacons (referred to as IBSS beacons) are used to advertise the network (which consists of all the nodes) as a whole while the infrastructure network beacons (referred to as BSS beacons) are generated by an AP and meant to advertise the existence of only that individual AP.
While related in general nature to mesh networks, ad hoc networks are not considered mesh networks within the context of this disclosure. Ad hoc networks can fundamentally be considered single hop networks because the network design is predicated on the assumption that all the nodes in the network can hear one another. Conversely, a wireless mesh network, as used herein, is a network capable of multi-hop wireless communications in which one node (or mesh point) may not necessarily hear all other network nodes.
Conventionally, beacon generation in ad hoc networks has been performed by all network stations. For example, each station picks a random delay at the end of a beacon interval and a beacon is sent when a timer expires provided that no other beacon has been transmitted in a current beacon generation window. This conventional mechanism depends on a Time Synchronization Function (TSF) shared between all ad hoc nodes, and which is feasible in a (one-hop) ad hoc network. However, for multi-hop mesh networks in which nodes may not be able to hear all other nodes present in the same network, a centralized TSF used for ad hoc networks cannot be relied on.
Consequently, a beaconing mechanism for wireless mesh networks that does not require time synchronization between nodes is desirable. Further, it would be advantages to have a beaconing mechanism that provides sufficient beacon coverage to facilitate effective mesh discovery via passive scanning by a station at any location within a mesh service area while preferably controlling the bandwidth overhead of beaconing in a dense mesh network.